# UA Restrictions

Zenlayer CDN allows you to configure a User-Agent blacklist identify and filter requests. This way, you can restrict access to CDN resources and improve service security.

User-Agent is an HTTP header. It contains the information about the client that makes the request, including the operating system (OS), OS version, browser, and browser version.

User-Agent blacklist: Requests whose User-Agent header has a value in the blacklist are rejected. The HTTP 403 status code is returned to the client.

<div align="left"><figure><img src="/files/jfdwqy0vYvqdKoI1ISp5" alt="" width="375"><figcaption></figcaption></figure></div>

### Block List

Expected result: Access to the above fields in the UA will be blocked.


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# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.console.zenlayer.com/welcome/content-delivery-network/domain-management/access-control/ua-restrictions.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.